In the fuel cell arts of hydrogen-oxygen fuel cells, it is known to provide gaseous hydrogen-containing fuel to a fuel cell stack by reforming hydrocarbon materials; for example, gasoline, diesel fuel, natural gas, or methane. A device for producing such hydrogen-containing fuel is known as a “reformer”, and the fuel itself is known in the arts as “reformate”.
Naturally occurring hydrocarbon starting materials typically contain small amounts of sulfur which can be present as H2S in reformate. A fuel cell stack such as a solid oxide fuel cell stack contains elements that are disabled, or “poisoned”, by small amounts of H2S in the reformate. Such a fuel cell stack suffers loss of power if the reformate fuel stream contains more than about 10 parts per billion (ppb) of sulfur; however, typical hydrocarbon sources can contain up to 2 parts per million (ppm) of sulfur, i.e., 200 times the desirable upper limit. Thus, from a practical standpoint, it is necessary to provide a device in the reformate stream between the reformer and the fuel cell stack to selectively remove a high percentage of the H2S from the reformate stream.
Efficient selective H2S adsorbers are known in the art, for example, nickel/alumina/rare earth compositions. Such materials can be highly efficient but have finite capacity and therefore must be regenerated or replaced periodically during operation of a fuel cell system. Removal and replacement of the adsorber material is the preferred procedure rather than in situ renewal. Such removal and replacement can be cumbersome. Moreover, since the adsorber operates in a hot zone environment where temperatures can exceed 750° C., a cool-down period is needed to return the temperature of the adsorber below a temperature suitable for handling of the adsorber, before removal and replacement of the adsorber can be completed, making such an exchange time-consuming.
What is needed in the art is an improved system for removal of H2S from a reformate stream requiring a minimum number of replacement parts and minimum operator training, and causing minimal fuel cell system downtime for replacement of an H2S adsorber.
It is a principal object of the present invention to simplify removal and replacement of an H2S adsorber in the hot zone of a fuel cell system.